The invention relates to an infrared light sensor chip with high measurement accuracy and a method for producing the infrared light sensor chip.
In order to detect gas, it is known to use infrared light that is in a wavelength range of 3 to 5 μm. The gas to be detected is irradiated with a light source that is suitable for emitting infrared light in this wavelength range. In this case a portion of the infrared light is absorbed by the gas, so that a residual light remains. The residual light can be measured with an infrared light sensor, with which the wavelength range and/or the intensity of the residual light can be detected and can be converted accordingly into an electrical signal. On the basis of the electrical signal, a suitable analysis allows the user to draw a conclusion regarding the type and the content of the detected gas.
The infrared light detector chip has typically a layer with pyroelectrically sensitive material, which is, for example, lead zirconate titanate (PZT). The layer is usually applied to a support membrane, which is normally made of silicon. Furthermore, the layer is electronically connected to electrodes, which are made, for example, of platinum or a nickel-chromium alloy that absorbs the infrared light radiation.
The infrared light sensor chip is used, for example, in a non-dispersive infrared light absorption analyzer (NDIR), which can be used for measuring gas concentrations. The output signal of the infrared light sensor chip that is based on a measurement of a gas concentration is highly dependent on the temperature, which the infrared light sensor chip has during the measurement, so that the measurement accuracy of the non-dispersive infrared absorption analyzer depends on the exact knowledge of the temperature of the infrared light sensor chip.
The infrared light sensor chip has a housing, in which the support membrane with the pyroelectrically sensitive layer and the electrodes is encapsulated for protection against harmful environmental effects. In order to draw a conclusion regarding the temperature of the infrared light sensor chip during the measurement, the non-dispersive infrared absorption analyzer is additionally provided with a temperature sensor, with which the temperature of the surrounding area of the infrared light sensor chip is currently measurable. Because the housing of the infrared light sensor chip is designed as small as possible for space-related reasons, the temperature sensor is arranged outside the housing. If the temperature sensor is attached to the housing, then the temperature of the housing is measured with the temperature sensor. As an alternative, the temperature sensor is arranged in close proximity to the housing, so that the ambient temperature of the housing is measured with the temperature sensor. In particular, if the ambient temperature changes with time, the situation generally arises that the temperature measured by the temperature sensor does not correlate with the temperature of the pyroelectrically sensitive layer, so that the results are measuring inaccuracies for the infrared light sensor chip.